The present invention relates to an activating composition for the plating of electrically insulative substrates and to a method for the plating of such substrates using said composition.
From the U.S. Pat. No. 4,248,632 is known a method for the metallization of non-conductive surfaces of organic polymers, based on the use of an activating solution containing a complex of a metal of the First or Eighth Subgroup of the Periodic Table of Elements, with an N-containing compound such as ammonia or a primary, secondary or tertiary amine, especially 2-aminopyridine.
That solution, prepared with an acidic to neutral pH, is applied onto the surface of the piece to be treated, which must be dipped subsequently in a reducing bath in order to reduce the complexed metal and deposit it onto the same surface, for its activation in view of the subsequent chemical metallization for reduction, or electroless reduction.
Pyridine complexes with various transition metals for the preparation of activating solutions to be used in the electroless plating of non-conductive surfaces, are also described in U.S. Pat. No. 3,523,874, whereas U.S. Pat. No. 4,734,299 describes complexes substantially of the same metals with amides.
The plating method comprises various steps, in each of which the non-conductive substrate is subjected to a treatment with chemical or physical agents.
After reach treatment, a washing is usually performed, to avoid the contamination of the subsequent bath with the solution of the previous one.
The known methods involve, in general, the disadvantage consisting in the easy removal of the activating solution from the substrate during the washing operation, due to the low adhesion of metal-amine or amide complex to the surface to be activated. Consequently, a few catalyst remains onto the substrate, and subsequent metallization for reduction is not adequately activated.
Purpose of the present invention is to eliminate or reduce the disadvantages of the known art, and in particular to provide an activating composition able to firmly adhere on the substrate surface to be metallized, pretreated with a step of a method also forming an object of the invention and ending with the electroless plating of the substrate.